1. Field of the Invention
The present invention relates to a tire air pressure warning apparatus for a vehicle and the like such as an automobile, airplane, and etc., and more particularly it relates to tire air pressure warning apparatus which can detect promptly any abnormality and give a warning by detecting the air pressure in a vehicle tire when the air pressure deviates from a predetermined pressure and an abnormal condition occurs, and thereby is feasible not only to prevent the fire from being damaged but also to keep the passengers safe.
2. Description of the Prior Art
When the air pressure within a tire of an automobile, airplane, and etc. is increased abnormally or reduced abruptly even without a puncture, naturally, damage of the tire can occur and also there is the possibility that the occupants can be endangered, so that it is a common knowledge that an appropriate inner air pressure of the tires must be maintained depending on the speed and the condition of road surface.
In view of the above, various tire air pressure warning devices for automatically detecting the inner air pressure of tires have been proposed heretofore, and typical devices utilize, a (1) current collector method wherein an air pressure detecting switch provided in a rotating tire portion and indicator provided in a stationary portion are connected with each other through a current collector ring mounted on the axle and a collector brush attached to the stationary portion; a (2) wireless method wherein a wireless frequency transmitter and transmitting antenna are provided on the tire rim and a signal is received by a receiving antenna and a receiver provided in a stationary portion; (3) and a resonance circuit method wherein an air pressure detecting switch, an antenna, and a tank circuit including inductance L and capacitance C are provided in a rotating tire portion, and a transmitter and a receiver are provided in a stationary portion, and which method makes use of the intermittent retransmission of the tank circuit responding to the variations in tire air pressure by transmitting intermittently the same frequency as the resonance frequency of the tank circuit. However, since the current collector ring method requires a mechanism sliding contact, degradation of performance tends to be caused by imperfect contact due to wearing of the members, dust and oil. The wireless method is complicated in structure since an electric source such as a generator, a battery or the like must be attached in the rotating tire portion as the power source for the transmitter, and there is also the problem that maintenance is troublesome, and particularly in case the of a generator, there is a fatal defect that the method loses its detecting function when the vehicle is stopped.
Furthermore, the third resonance circuit method employs a complicated mechanism, deviations in resonance tend to occur, detecting accuracy is a problem, and therefore is of less general usability.
As mentioned above, various prior art warning devices all have a problem in the permanent stability of the detecting function, and there are problems such as an increase in cost due to the complexity of the device, the intricacy of maintenance and the like. In fact they are not used in general.